Electronic paper was developed in 1992 at Xerox Palo Alto Research Center (PARC) by N. Sheridan as a new type of display technology. According to M. E. Howard, E. A. Richley, R. Sprague, and N. K. Sheridon, “GYRICON electronic paper”, J. Soc. for Information Display, Vol. 4, pp. 215, 1998, this news type of display technology was called “GYRICON” and combined advantages of regular paper and electronic displays. Sheridan fabricated a rubber like sheet containing thousands of tiny balls. Half of the balls where white colored and were positively charged; the other half were black and had no charge. When a bias was applied, the balls were able to rotate and generate a black-and-white pattern. The most important difference to conventional electronic displays was that power was only consumed when the balls rotated; in other words, power was only consumed when the displayed pattern changed. The “GYRICON” technology was not pursued by Xerox and remained dormant until the mid-1990's. In 1999, Xerox teamed with 3M Corporation to mass-produce GYRICON e-paper but this effort is now discontinued.
In 1998, J. Jacobson of MIT published a Nature article with a slightly different approach to electronic paper (see B. Comiskey, J. D. Albert, H. Yoshizawa, J. Jacobson, “An electrophoretic ink for all-printed reflective electronic displays”, Nature, vol. 394, pp. 253, 1998). Jacobson's approach comprised transparent micro-capsules filled with blue dye and white titanium oxide (TiO2) particles. The diameters of the micro-capsules were approximately one hundred micrometers (100 μm) and made of low-molecular-weight polyethylene (see FIG. 1). The TiO2 particles were negatively charged and could be moved within the microsphere by applying an external bias. In response to an electrical charge, the TiO2 particles moved to the top or bottom of the capsule, thereby creating light or dark colored spots (see FIG. 2). Gray-tones were created by moving particles within the micro-sphere. The charge needed to “flip” one TiO2 particle can be as low as q=2.6×10−18, C=16 e− for a; given solution. As in the GYRICON technology, power is only consumed when the particles are moved within the sphere. MIT commercialized this technology and founded E-INK, Inc. (hereafter “E-INK”). E-INK electronic paper is inexpensive and has been integrated into consumer products. FIG. 3 shows a LEXAR USB drive with electronic paper from E-INK includes an indicator of how much data is stored on the device. The work of J. Jacobson sparked wide interest in electrophoretic ink (i.e., electronic paper).
Electronic paper is comprised of micro-containers filled with charged particles (with diameters ranging from approximately 100 nanometers (nm) to a few micrometers (μm)), preferably between from about 200 nm to about 5 micrometers. These particles are charged and form a stable colloidal solution (i.e., no sedimentation of particles over time). An external electric field can move the particles within the micro-container and change the overall color of the device. Power is only consumed when the display appearance changes. Several research groups and companies modified Jacobson's approach; one example is “SiPix, Inc.” (hereafter “SIPIX”) (see http://www.sipix.com/technology/microcup.html). SIPIX uses microscale containers made from a flexible polymer. These containers act as hosts for the particles (see FIG. 4). The production is scaled up to large area flexible displays.
The mechanism of particle movement due to an external voltage within the electronic paper is still under investigation. Early investigations of electronic paper revealed that electrophoretic forces alone could explain the particle movement. Today, most researchers believe that the particle movement in electronic paper can be described and/or explained by electrophoretic and dielectrophoretic forces, where the influence of the electrophoretic forces dominate.
The property of the stable colloidal solution formed in the micro-container, containing particles is directly correlated to the operation and sensitivity of the device. The liquid layer surrounding the particle exists as two parts; an inner region (Stern layer) where the ions are strongly bound and an outer (diffuse) region where the ions are less firmly associated. Within the diffuse layer, there is a notional boundary inside which the ions and particles form a stable entity. When a particle moves (such as due to gravity or an external electric field), ions within the boundary move the particle. Those ions beyond the boundary stay with the bulk dispersant. The potential at this boundary (surface of hydrodynamic shear) is the zeta potential. The magnitude of the zeta potential gives an indication of the potential stability of the colloidal system and their mobility The general dividing line between stable and unstable suspensions is generally taken at either +30 or −30 millivolts (mV). Particles with zeta potentials more positive than +30 mV or more negative than −30 mV are normally considered stable. The zeta potential can be adjusted by the colloidal solution parameters, for example the pH value of the overall electrolyte conductivity modifies the zeta-potential. An important consequence of the existence of electrical charges of particles is that they interact with an applied electric field. These effects are collectively defined as electrokinetic effects. There are two effects which affect the particle's motion in the micro-container: The dominating force is electrophoreses: the movement of a charged particle relative to the liquid it is suspended in under the influence of an applied electric field. Furthermore, to a much less extent, dielectrophoresic force plays a role: Dielectrophoresis describes the movement of polarizable particles in a non-uniform electric field. Some non-uniform electric fields can fore due to shape of the micro-container.
Common electronic displays like LCDs (liquid crystal displays) require constant power. Electrophoretic displays are now commonly used in consumer electronics, like Amazon's Kindle. When the Electronic paper is irradiated, the incoming gamma-rays interact with the embedded particles and generate a recoil electron. This recoil electron physically leaves the particle and thereby changing particle's charge. Particles inside the micro-container form a stable colloidal solution. The particles' position and mobility within the micro-container is a direct function of their charge. Since the basic sensing principle of the electronic paper is based on charging particles within a transparent micro-container, then the electronic paper can also be used to detect chemical or biological agents with a sensing reaction that involves charge transfer.
Currently, members of the military, police, fire, and medical first responders require reliable indicators of their exposure to doses of dangerous radiological, chemical and/or biological agents, if they are operating in environments that might contain high energy radiation, chemical or bio-chemical agents, as might be present in conjunction with terrorist attacks and/or industrial attacks, where bad actors use dirty bombs containing radioactive materials or target nuclear power plants for sabotage and/or destruction or use contraband nuclear weapons, or environments where industrial accidents have occurred. This invention materially contributes to countering such terrorism, by providing immediate real time indications of CBR agents. Thus, minimizing the ability of terrorists to influence the policy of the government of the United States with tactics directed at intimidation and coercion by inflicting pain, suffering and death on US citizens and first responders through the use of undetected CBR weapons of mass destruction.
Radiation detection can be broadly grouped into two types of instruments: (i) radiation detectors and (ii) dosimeters. On the one hand, radiation detectors like the traditional Geiger Counter tend to be big and bulky. These devices cannot be worn on regular clothing. On the other hand, wearable dosimeters, such as a film badge dosimeter, do not give instant warning and can only be used once. Pen dosimeters have been in use for approximately 50 years but are bulky and require constant re-calibration.
Semiconductor based dosimeters require constant battery power. Constant power consumption is problematic due to limited battery lifetime and weight.
None of the current devices meet the following requirements: re-usable, provides instant indication of dosage, exhibits ultra-low power and weight, and is capable of being integrated into a regular uniform.
Currently, there are no known radiation dosimeters based on electrophoretic displays (i.e., based on electronic paper).
Currently, there are no known chemical and/or bio-chemical sensors based on electrophoretic displays.
Therefore, the need exists for a radiation dosimeter based on electrophoretic displays.
Furthermore, the need exists for a radiation sensor and/or bio-chemical sensor, based on electrophoretic displays, which are re-usable, provide instant indications of dosage, exhibit ultra-low power and weight, and are capable of being integrated into a regular uniform.